BIOL204 Cons Gen Session 1 Flashcards
What are the evolutionary processes that effect the genetic diversity of populations? (4)
- Mutation
- Selection
- Gene Flow
- Genetic Drift
Demographic Stochasticity
Fluctuations in Birth/Death rate, immigration/emigration, disease ect. This effects population size, small populations are more vulnerable to these changes
Genetic Load
A measure of the extent that average fitness, viability or other favourable attributes of a population is decreased by the factor under consideration (Encyclopedia of Genetics, 2001) SIMPLE: The reduction in beneficial genetic diversity after an event.
Frequency or Density dependent selection
Population growth rates are regulated by the density of . a population. POSITVIE= passanger pigeon, more individuals in flock increases foraging vision & opportunity, NEGATIVE= plants use up available nutrients in environment.
Directional Selection
One extreme of trait is selected against, leading to a shift in characteristics. eg. Giraffe necks
Directional selection is a type of natural selection in which the phenotype (the observable characteristics) of the species tends toward one extreme rather the mean phenotype or the opposite extreme phenotype. (look up graphs)
Disruptive or Diversifying Selection
Individuals with an intermediate trait are selected against- eg. some pollinators have a reduced preference to a medium plant height, produces polymorphic species traits
Stabilising or balancing selection
Extremes of a population are selected against, bell curve graph
Essential Reading
Frankham R (2005) Genetics and extinction. Biological Conservation 126(2), 131-140.
Frankham, R, Ballou JD and Briscoe DA (2010) Genetic consequences of small population sizes. Chapter 8 in Introduction to Conservation Genetics. 2nd Edn, Cambridge University Press.
Mills LS (2013) Genetic variation and fitness in wildlife populations Chapter 9 in Conservation of Wildlife Populations. 2nd Edn, John Wiley & Sons, Ltd
What is conservation genetics?
the use of genetic theory and techniques to reduce the risk of extinction in threatened species (frankham et al. 2004)
why can existing in a small population be a problem for organisms?
1) pops are more vulnerable to random fluctuations in birth, death, em or im. (demographic stochasticity)
2) There is reduced genetic diversity, so have lower adaptive potential and higher ‘genetic load’.
Give a definition of a mutation
A change in the DNA sequence or chromosome in the transmission of genetic information from parent to progeny
How can you measure mutation rates in organisms? (5)
per base per cell per organism per genome per generation
When thinking about the overall impact of mutation rate on genetic diversity, what should we note?
- There is variation in mutation rates between: bases, chromosomes, tissue types of multicellular organisms, sexes and species.
- In regions of the genome that code for proteins or that have other key function, the vast majority of mutations are immediately selected out of the population as they create a disadvantage to the organism: those individuals either die, or survive but are unable to breed.
- Quantifying mutation rates is an active and ongoing field of research investigating what the differences and what is driving those differences (Hodgkinson and Eyre-Walker, 2011)
What is the overall impact of mutation rate on genetic diversity?
From the perspective of evolutionary change in populations, it increases genetic diversity but at a relatively slow rate.
Define ‘Selection’
differential contribution of genotypes to the next generation due to differences in survival and reproduction.
Selection can either maintain or decrease the genetic diversity of populations: its effects are complex and often difficult to predict.
